This invention relates to hydraulic piston and cylinder assemblies for affecting translatory to and fro motion, and more particularly to such an assembly constructed to resist forces that are transverse to the direction of motion of the piston.
In the steering of watercraft, a hydraulic cylinder and piston assembly is often employed to move a pivoting element such as an outboard motor or an outdrive for an inboard engine. The cylinder links a stationary point on the transom to a point on the pivoting element beyond the pivot axis. Hydraulic controls shorten or lengthen the cylinder assembly to pivot the element about the pivot axis. In the case of high power marine propulsion units, there may be forces as high as one thousand horsepower at the propeller of the pivoted element. On the water, these forces may be applied erratically in almost any direction. For example, when in straight forward motion, a rotating fully immersed propeller produces a resultant of forces that is in line with the keel. The lower blades produce a lateral force in one direction that are cancelled by the upper blades producing a lateral force in the opposite direction. However, when the propeller is lifted half way out of the water, the upper blades hit only air and provide no cancelling force. Consequently, the propulsion unit is subjected to a sudden strong lateral force. In order to withstand these lateral forces, a marine hydraulic cylinder assembly must be made very large and heavy, because the lateral forces put excessive stress on the assembly.